In known foldable, flat ball point pens, the rotary axis of the pen is often located in the middle area of one of the parts. This part may be configured as a U-frame, open at one end, which makes the device unstable and inclined to break. Also, as a result, prior art pens when in use, may be quite short when a longer pen, according to the present invention, rests more comfortably in the hand of the writer. The prior art also teaches ball point pens which may be folded in the same manner as a clasp pocket knife which although providing a more usable instrument, tends to be clumsy to carry, particularly in a shirt pocket.